Mr Saunders, whose widow Elizabeth is from Teesside, had begun firing shots at about 4.40pm on May 6, 2008, following a drinking binge.

The officer, known only as AZ 12, told an inquest he thought Mr Saunders was going to kill colleagues. He told Westminster Coroner’s Court he had been stationed as “a show of force” in cover at garden level at a house in Bywater Street, near Mr Saunders’ home.

He described how after Mr Saunders opened the window and was “lowering the weapon towards my colleagues” on the roof of a neighbouring house.

Asked if he shot Mr Saunders in self-defence, he said: “No, in defence of others. I thought he was going to kill them.”

He told the inquest that what he did was “absolutely necessary”.

“I felt there was an imminent threat to their life. If I had left it too late, they could have been dead. It was my duty as a police officer to defend my colleagues.”

Another officer, known only as AZ 15, told the hearing of an exchange of gunfire early in the stand-off. The officer went to another house in Bywater Street and climbed up to a bedroom.

“I noticed straight away that the window had damage, and it appeared to be either birdshot or pellets from a shotgun,” he said.

“I made it clear to the occupants of the address to stay in the hallway and positioned myself to the left-hand side of the window.”

At first he thought that the gunman was in the garden but then saw him standing at a window.

“I could see he was carrying a long-barrelled weapon. Initially it was facing towards the ground.

“At the point where I noticed he was carrying the weapon, it was leveled in the direction of the area I was in and a shot was discharged towards my direction.”

He became aware that one of the occupants of the house had come into the room. “I feared for the safety of the person in the room, so until I could assess where that person was, I discharged two shots from my weapon.”